Actually, sweetie, it's NOT a power listed. It's an explanation for a power listed, which is the power to collect taxes, levies, duties, etc. Perhaps if you read the entire Article, rather than your highly expurgated and mangled cherry-picking, you would know that.
Actually, darling, it is listed right there in Section 8, the very first of the listed powers of Congress, each of which is prefaced by "To...", each of which is set off by a semicolon:
The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;
To borrow money on the credit of the United States;
To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes;
etc.
And I agree, it is an explanation of a power, a power to provide for the general welfare as well as the other things identified in the clause.
Providing for the general welfare can't be a power AND the explanation for itself. Is English not your first language?
Let me translate for the education-impaired:
. . . Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States;
". . . Imposts and excises,
IN ORDER to pay the debts and provide for the common defense . . ." is what that actually means. You will notice that each of the delineated powers, such as "To lay and collect taxes . . ." and "To borrow money . . ." and "To regulate commerce . . ." is listed in its own separate paragraph, the 18th-century equivalent of bulleting. However, ". . . to pay debts . . ." is not. It's listed as part of the paragraph concerning taxes, excises, etc. Why? Because it's not a power being granted. It's an explanation of WHY the power to collect taxes and such is being granted.
The Article explains what it means by "general welfare" when it specifies duties of Congress, just as it goes on to explain what it means by "common defense" when it lays out the specific military services Congress can set up and by what method. Nothing in the original text of the Constitution is written to be a blank
carte blanche of power to any branch of government.
As I said, learn to read for context.